This document discusses polymer membrane permeation controlled drug delivery systems. It defines controlled release as delivering drugs at predetermined rates over long periods from a single dose. Controlled release implies predictable and reproducible drug release kinetics. A key example is a system where a drug reservoir is covered by a rate-controlling polymeric membrane. The membrane thickness and drug properties determine the release rate. Applications include the Norplant implant and Ocusert ocular insert.

1. “POLYMER MEMBRANE PERMEATION CONTROLLED
DRUG DELIVERY SYSTEM”

2. Sustained release, sustained action, controlled release,
extended action, timed release dosage forms are the terms
used to identify drug delivery systems that are designed to
achieve a prolonged therapeutic effect by continuously
releasing medication over an extended period of time after
the administration of single dose.
 The term “Controlled release” has become associated
with those systems from which therapeutic agents may be
automatically delivered at predefined rates over a long
period of time.
But, there are some confusion in terminology between
“Controlled release” & “Sustained release”

3. Sustained Release :
 The term sustained release has been constantly used to describe
a pharmaceutical dosage form formulated to retard the release of
a therapeutic agent such that its appearance in the systemic
circulation is delayed &/or prolonged & its plasma profile is
sustained in duration.
Controlled Release :
 This term on the other hand, has a meaning that goes beyond
the scope of sustained drug action.
 It also implies a predictability & reproducibility in the drug
release kinetics, which means that the release of drug ingredient
from a controlled delivery system proceeds at a rate profile that is
not only predictable kinetically, but also reproducible from one
unit to another.

4.  An ideal controlled drug delivery system is the one which
delivers the drug at a predetermined rate, locally or
systematically for a specified period of time.

5. Biopharmaceutic Characteristics of the Drug
Molecular weight, Aqueous solubility, Partition coefficient,
Drug Pka and Ionization, Route of administration, Drug stability
etc
Pharmacokinetic Characteristics of the Drug
Absorption rate, Elimination Half-Life, Rate of metabolism etc.
Pharmacodynamic Characteristics of the
Drug
Therapeutic Range, Therapeutic index, Plasma concentration
response relatioship

6. These are some of the first materials selected for delivery
systems bases on their intended non-biological physical
properties:
 Polyurethanes for elasticity
 Polysiloxanes for insulating ability
 Polymethyl methacrylate for physical strength and
transparency
 Polyvinyl alcohol for hydrophilicity and swelling
 Polyvinyl pyrrolidone for suspension capabilities

7. These polymers became usable in controlled delivery due to
their inert physical characteristics and being free of
leachable impurities
 Poly 2-hydroxy ethyl methacrylate
 Poly N-vinyl pyrrolidone
 Polyvinyl alcohol
 Polyacrylic acid
 Polyethylene glycol
 Polymethacrylic acid

8. Number of approaches have been developed to achieve
controlled administration of drugs via implantation
(1) Controlled drug delivery by diffusion process
 Diffusion of the drug out of the device or solvent into
the polymer ultimately contributes to the drug-release
process
 Release of the drug from the device is preprogrammed
at a specific rate profile
 This is accomplished by a system design which
controls molecular diffusion of drug in or and/or
across barrier medium surrounding the system
 This systems can be further sub classified in to number
of classes

9. Based on their technical sophistication :
 Rate preprogrammed drug delivery system
 Activation-modulated drug delivery system
 Feedback-regulated drug delivery system
 Site targeting drug delivery system

10. In this group , the release of drug molecule from the
system has been preprogrammed at specific rate profile.
They can be classified as
1. Polymer membrane permeation-controlled drug
delivery system
2. Polymer matrix diffusion-controlled drug delivery system
3. Micro-reservior partition-controlled drug delivery
system

11. In this type, drug is totally or partially encapsulated within
drug reservoir.
Its drug release surface is covered by a rate-controlling
polymeric membrane having a specific permeability.
Drug reservoir may exist in solid, suspension or solution
form drug reservoir
Polymeric membrane
Drug contained in a formulation

12. Polymer membrane permeation- controlled drug
delivery using
1. Non porous membrane
2. Micro porous membrane
3. Semi permeable membrane

13. Polymer Membrane Permeation-Controlled Drug Delivery
System
 The dug reservoir can exist in to a solid , suspension or in a
solution form and polymeric membrane fabricated in the formof
non porous{homogenous or heterogeneous}, micro porous or
semi-permeable membrane.
 Encapsulation of drug formulation in to the reservoir
compartment can be done by:
1. Injection molding
2. Spray coating
3. microencapsulation
 Different shapes of the systems like sphere , cylinder or sheet can
be fabricated
 An example of this type of implantable drug delivery system is A
Norplant Subdermal Implant And Ocusert Systems.

14. Fig: Diagrammatic representation of membrane
permeation controlled system in which drug
reservoir is stacked between the layers of drug
impermeable plastic laminate and rate controlling
membrane and below which the adhesive layers
faces the skin surface.

15. Release of drug molecules is controlled by :
Partition coefficient of the drug molecule.
Diffusivity of the drug molecule.
The thickness of the rate controlling membrane.

16. The rate of drug release is defined by,
Q = Km/r Ka/m DdDm x CR
t Km/r Dmhd + Ka/m Ddhm
Where,
Km/r & Ka/m = partition coefficient of the drug molecule
from reservoir to rate controlling membrane & from
membrane to aq. Layer respectively.
Dd & Dm = diffusion coefficient of rate controlling
membrane & aqueous diffusion layer respectively.
hm & hd = thickness of rate controlling membrane &
aqueous diffusion layer respectively.
CR – drug conc. In reservoir compartment.

17. Ocusert system
 In this device, the solid drug reservoir, which is a thin disc of
pilocarpine alginate, is sandwiched between two transparent sheets of
microporous membrane fabricated from ethyvinly acetate copolymer.
 It is designed permit the tear fluid to penetrate the microporous
membranes, to dissolve and to carry out pilocarpine at a constant rate
of 20 to 40 mcg/hr for weekly management of glaucoma.

18. • Norplant is implanted under the skin in the upper arm
of a woman, by creating a small incision.
• inserting the capsules in a fanlike shape.
• Insertion of Norplant usually takes 15 minutes
• the contraceptive works within 24 hours and lasts up to
five years.

19.  The drug reservoir is a
suspension of progesterone &
barium sulphate in silicone
medical fluid & is
encapsulated in the vertical
limb of a T-shaped device
walled by a non-porous
membrane of ethylene-vinyl
acetate co-polymer.
 It is designed to deliver
natural progesterone
continuously in uterine cavity
at a daily dosage rate of at
least 65 μg/day to achieve
contraception for 1 year.
Ex. Progestasert IUD

20.  Drug Reservoir :
 dispersed on solid polymer matrix eg. polyisobutylene.
 Suspended in unleachable viscous liquid medium eg.
Silicone fluid.
Dissolved in solvent.
Rate controlling Membrane: Microporous, Nonporous. Eg.
Ethylene-Vinyl acetate copolymer.
Adhesive Layer: Thin layer, adhesive, drug compatible,
hypoallergic, eg. Silicone adhesive.

21. Polymeric Membrane Permeation Controlled Release
Drug Delivery System
Advantages :
1. Less fluctuation in drug blood levels.
2. Frequency reduction in dosing.
3. Improved patient convenience & compliance.
4. Increased safety margin of the high potency drugs.
5. Reduction in total health care cost.
Disadvantages :
1. Decreased systemic availability in comparison to
immediate release conventional dosage forms.
2. Poor in vivo – in vitro correlation.
3. Possibility of dose dumping.
4. Retrieval of drug is difficult.
5. Higher cost of formulation.